Optimising energy efficiency

As a leading global provider of hydraulic systems, HANSA‑FLEX applies extensive quality controls to ensure that all hose lines meet the highest standards at all times, even under extreme conditions. In the central Quality Assurance department in Bremen, four in-house pressure impulse test benches are available to carry out the required extensive testing. These test benches have a connected load of approx. 30-80 kW. In its role as the operator HANSA‑FLEX has succeeded by means of a retrofit in reducing the operating costs of a testing machine by over 50%. 

Like many other operators of hydraulic systems, HANSA‑FLEX has set itself the goal of examining the feasibility of reducing operating costs by lowering energy requirements. This analysis shows that there is considerable potential for electricity savings on two of the four in-house pressure impulse test benches. But how can operators of hydraulic systems even tell whether there is potential for increasing energy efficiency in the case of the machine or test bench? 
 
This question can be answered as a first step by the following tests: 

• Does the oil temperature in the tank often climb higher than 60 °C? 
• Are some valves in the hydraulic system significantly hotter than others? 
• Are negative/pressure loads often moved (load direction acts in the direction of movement)? 
• Are flow control valves (throttles, flow regulating valves, proportional valves) installed? 
• Are several consuming units supplied simultaneously by one pump? 

 
If the answer to one or more of these questions is “yes”, a system analysis may be worthwhile. Often an over-dimensioning of the volume flow or pressure - in the worst case both – can be determined. In the case of the HANSA‑FLEX pressure impulse test benches, the first two points in particular apply. After this simple evaluation of the savings potential, the hydraulic system is analysed in detail to optimise energy efficiency. 

The first step in the analysis is to examine the design and function of the system, or in this case the HANSA‑FLEX pressure impulse test bench. This test bench is used to perform pressure impulse tests in accordance with ISO 6803 (see Fig. 1). Up to six hose lines can be tested simultaneously in the test chamber. The pressure impulse is generated with a pressure intensifier. An impulse is divided into four areas (see Fig. 2) which are implemented with the pressure intensifier as follows: 
 
(I) Extending the pressure intensifier leads to a pressure build-up (high pressure = test pressure = red curve) in the hose lines to be tested. 
(II) The test pressure and therefore the position of the pressure intensifier is maintained. 
(III) If the test pressure is to be reduced again, the pressure intensifier must be retracted. 
(IV) At the end of a pressure impulse cycle, the hose lines to be tested are flushed with a pressure of 0-10 bar.

The direction of movement of the pressure intensifier in this test bench is achieved with a pilot-controlled 4/3-way valve (switching valve). The supply pressure or low pressure (blue curve) for this valve and consequently also for the pressure intensifier is constant all the time. According to the transmission ratio of the pressure intensifier, the low pressure is set proportionally to the test/high pressure. To implement the variable low pressure, a fixed displacement pump in combination with a proportional pressure relief valve is used on this test bench. In this system the volume flow not required by the pressure intensifier must be discharged with the set low pressure via the proportional pressure relief valve.

In the second step of the analysis, the power flows for the pressure impulse test of four HD410 hose lines are determined (see Fig. 3). The diagram of the power flows shows a supplied electrical power of approx. 30 kW, with only 3 kW being used by the pressure intensifier. The greatest losses occur at the proportional pressure relief valve with 8 kW. Due to these and other losses, a correspondingly large amount of cooling power has to be applied, so that the supplied electrical power of the cooling unit is just under 9 kW. After the quantitative determination of the power consumption, suitable measures to reduce the losses can now be worked out. One of the most decisive measures is to replace the fixed displacement pump with a variable displacement pump. This change alone can completely eliminate the 8 kW power loss via the proportional pressure relief valve. These and other measures were implemented by modifying the hydraulic system.

In order to assess the energy efficiency optimisation, the pressure impulse test of six HD410 hose assemblies was then carried out with the same test parameters (see Fig. 4). The fact that this time six instead of four hose lines were tested as before the conversion can be seen from the slightly higher effective power of the pressure intensifier. Although more hose lines were tested after the conversion, the measures taken enabled the supplied electrical power to be reduced by over 50 %, from 30.1 kW to 13.4 kW. The energy saved for this operating point amounts to 120,000 kWh per year (operating time 7,200 operating hours annually, saving 16.7 kW). At an electricity price of 10 ct/kWh, this results in an annual saving in electricity consumption of 12,000 €.

The International Hydraulics Academy (IHA) will be happy to advise you on questions concerning the energy efficiency of your hydraulic systems. The consultation includes an individual system analysis as well as the development of solution proposals for a retrofit. The Federal Ministry of Economics and Energy subsidises by up to 40% the costs of these measures to save energy and reduce carbon dioxide emissions (see KfW Reconstruction Loan Corporation Credit 295 Module 4: energy-related optimisation of installations and processes).